Subject: Re: SQL/JSON revisited

From: Alvaro Herrera <[email-masked]>
Date: Fri, 31 Mar 2023 18:49:40 +0200

Here's v14 of the IS JSON predicate.  I find no further problems here
and intend to get it pushed later today.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"Siempre hay que alimentar a los dioses, aunque la tierra esté seca" (Orual)
>From 998ec6bd170e83cdb916ab40bec5cac56ecd1d81 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <[email-masked]>
Date: Fri, 31 Mar 2023 18:47:51 +0200
Subject: [PATCH v14] SQL/JSON: support the IS JSON predicate

This patch introduces the SQL standard IS JSON predicate. It operates
on text and bytea values representing JSON, as well as on the json and
jsonb types. Each test has IS and IS NOT variants and supports a WITH
UNIQUE KEYS flag. The tests are:

IS JSON [VALUE]
IS JSON ARRAY
IS JSON OBJECT
IS JSON SCALAR

These should be self-explanatory.

The WITH UNIQUE KEYS flag makes these return false when duplicate keys
exist in any object within the value, not necessarily directly contained
in the outermost object.

Author: Nikita Glukhov <[email-masked]>
Author: Teodor Sigaev <[email-masked]>
Author: Oleg Bartunov <[email-masked]>
Author: Alexander Korotkov <[email-masked]>
Author: Amit Langote <[email-masked]>
Author: Andrew Dunstan <[email-masked]>

Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.

Discussion: https://postgr.es/m/CAF4Au4w2x-5LTnN_bxky-mq4=[email-masked]
Discussion: https://postgr.es/m/[email-masked]
Discussion: https://postgr.es/m/[email-masked]
Discussion: https://postgr.es/m/abd9b83b-aa66-f230-3d6d-734817f0995d%40postgresql.org
---
 doc/src/sgml/func.sgml                        |  80 +++++++
 src/backend/executor/execExpr.c               |  13 ++
 src/backend/executor/execExprInterp.c         |  99 +++++++++
 src/backend/jit/llvm/llvmjit_expr.c           |   6 +
 src/backend/jit/llvm/llvmjit_types.c          |   1 +
 src/backend/nodes/makefuncs.c                 |  19 ++
 src/backend/nodes/nodeFuncs.c                 |  26 +++
 src/backend/parser/gram.y                     |  70 ++++++-
 src/backend/parser/parse_expr.c               |  76 +++++++
 src/backend/parser/parser.c                   |   3 +
 src/backend/utils/adt/json.c                  | 132 +++++++++++-
 src/backend/utils/adt/jsonfuncs.c             |  20 ++
 src/backend/utils/adt/ruleutils.c             |  37 ++++
 src/include/catalog/catversion.h              |   2 +-
 src/include/executor/execExpr.h               |   8 +
 src/include/nodes/makefuncs.h                 |   3 +
 src/include/nodes/primnodes.h                 |  26 +++
 src/include/parser/kwlist.h                   |   1 +
 src/include/utils/json.h                      |   1 +
 src/include/utils/jsonfuncs.h                 |   3 +
 src/interfaces/ecpg/preproc/parse.pl          |   1 +
 src/interfaces/ecpg/preproc/parser.c          |   3 +
 .../ecpg/test/expected/sql-sqljson.c          |  73 +++++--
 .../ecpg/test/expected/sql-sqljson.stderr     |  86 +++++---
 .../ecpg/test/expected/sql-sqljson.stdout     |   8 +
 src/interfaces/ecpg/test/sql/sqljson.pgc      |  17 ++
 src/test/regress/expected/sqljson.out         | 198 ++++++++++++++++++
 src/test/regress/sql/sqljson.sql              |  96 +++++++++
 28 files changed, 1039 insertions(+), 69 deletions(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 38e7f46760..918a492234 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -16005,6 +16005,86 @@ table2-mapping
     </tgroup>
    </table>
 
+  <para>
+   <xref linkend="functions-sqljson-misc" /> details SQL/JSON
+   facilities for testing JSON.
+  </para>
+
+  <table id="functions-sqljson-misc">
+   <title>SQL/JSON Testing Functions</title>
+   <tgroup cols="1">
+    <thead>
+     <row>
+      <entry role="func_table_entry"><para role="func_signature">
+        Function signature
+       </para>
+       <para>
+        Description
+       </para>
+       <para>
+        Example(s)
+      </para></entry>
+     </row>
+    </thead>
+    <tbody>
+     <row>
+      <entry role="func_table_entry"><para role="func_signature">
+        <indexterm><primary>IS JSON</primary></indexterm>
+        <replaceable>expression</replaceable> <literal>IS</literal> <optional> <literal>NOT</literal> </optional> <literal>JSON</literal>
+        <optional> { <literal>VALUE</literal> | <literal>SCALAR</literal> | <literal>ARRAY</literal> | <literal>OBJECT</literal> } </optional>
+        <optional> { <literal>WITH</literal> | <literal>WITHOUT</literal> } <literal>UNIQUE</literal> <optional> <literal>KEYS</literal> </optional> </optional>
+       </para>
+       <para>
+        This predicate tests whether <replaceable>expression</replaceable> can be
+        parsed as JSON, possibly of a specified type.
+        If <literal>SCALAR</literal> or <literal>ARRAY</literal> or
+        <literal>OBJECT</literal> is specified, the
+        test is whether or not the JSON is of that particular type. If
+        <literal>WITH UNIQUE KEYS</literal> is specified, then any object in the
+        <replaceable>expression</replaceable> is also tested to see if it
+        has duplicate keys.
+       </para>
+       <para>
+<programlisting>
+SELECT js,
+  js IS JSON "json?",
+  js IS JSON SCALAR "scalar?",
+  js IS JSON OBJECT "object?",
+  js IS JSON ARRAY "array?"
+FROM (VALUES
+      ('123'), ('"abc"'), ('{"a": "b"}'), ('[1,2]'),('abc')) foo(js);
+     js     | json? | scalar? | object? | array? 
+------------+-------+---------+---------+--------
+ 123        | t     | t       | f       | f
+ "abc"      | t     | t       | f       | f
+ {"a": "b"} | t     | f       | t       | f
+ [1,2]      | t     | f       | f       | t
+ abc        | f     | f       | f       | f
+</programlisting>
+       </para>
+       <para>
+<programlisting>
+SELECT js,
+  js IS JSON OBJECT "object?",
+  js IS JSON ARRAY "array?",
+  js IS JSON ARRAY WITH UNIQUE KEYS "array w. UK?",
+  js IS JSON ARRAY WITHOUT UNIQUE KEYS "array w/o UK?"
+FROM (VALUES ('[{"a":"1"},
+ {"b":"2","b":"3"}]')) foo(js);
+-[ RECORD 1 ]-+--------------------
+js            | [{"a":"1"},        +
+              |  {"b":"2","b":"3"}]
+object?       | f
+array?        | t
+array w. UK?  | f
+array w/o UK? | t
+</programlisting>
+      </para></entry>
+     </row>
+    </tbody>
+   </tgroup>
+  </table>
+
   <para>
    <xref linkend="functions-json-processing-table"/> shows the functions that
    are available for processing <type>json</type> and <type>jsonb</type> values.
diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c
index 6c5a378029..4c6700de04 100644
--- a/src/backend/executor/execExpr.c
+++ b/src/backend/executor/execExpr.c
@@ -2370,6 +2370,19 @@ ExecInitExprRec(Expr *node, ExprState *state,
 			}
 			break;
 
+		case T_JsonIsPredicate:
+			{
+				JsonIsPredicate *pred = (JsonIsPredicate *) node;
+
+				ExecInitExprRec((Expr *) pred->expr, state, resv, resnull);
+
+				scratch.opcode = EEOP_IS_JSON;
+				scratch.d.is_json.pred = pred;
+
+				ExprEvalPushStep(state, &scratch);
+				break;
+			}
+
 		case T_NullTest:
 			{
 				NullTest   *ntest = (NullTest *) node;
diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index 5e55592f80..4cd46f1717 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -73,6 +73,7 @@
 #include "utils/expandedrecord.h"
 #include "utils/json.h"
 #include "utils/jsonb.h"
+#include "utils/jsonfuncs.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/timestamp.h"
@@ -477,6 +478,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 		&&CASE_EEOP_HASHED_SCALARARRAYOP,
 		&&CASE_EEOP_XMLEXPR,
 		&&CASE_EEOP_JSON_CONSTRUCTOR,
+		&&CASE_EEOP_IS_JSON,
 		&&CASE_EEOP_AGGREF,
 		&&CASE_EEOP_GROUPING_FUNC,
 		&&CASE_EEOP_WINDOW_FUNC,
@@ -1521,6 +1523,14 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 			EEO_NEXT();
 		}
 
+		EEO_CASE(EEOP_IS_JSON)
+		{
+			/* too complex for an inline implementation */
+			ExecEvalJsonIsPredicate(state, op);
+
+			EEO_NEXT();
+		}
+
 		EEO_CASE(EEOP_AGGREF)
 		{
 			/*
@@ -3921,6 +3931,95 @@ ExecEvalJsonConstructor(ExprState *state, ExprEvalStep *op,
 	*op->resnull = isnull;
 }
 
+/*
+ * Evaluate a IS JSON predicate.
+ */
+void
+ExecEvalJsonIsPredicate(ExprState *state, ExprEvalStep *op)
+{
+	JsonIsPredicate *pred = op->d.is_json.pred;
+	Datum		js = *op->resvalue;
+	Oid			exprtype;
+	bool		res;
+
+	if (*op->resnull)
+	{
+		*op->resvalue = BoolGetDatum(false);
+		return;
+	}
+
+	exprtype = exprType(pred->expr);
+
+	if (exprtype == TEXTOID || exprtype == JSONOID)
+	{
+		text	   *json = DatumGetTextP(js);
+
+		if (pred->item_type == JS_TYPE_ANY)
+			res = true;
+		else
+		{
+			switch (json_get_first_token(json, false))
+			{
+				case JSON_TOKEN_OBJECT_START:
+					res = pred->item_type == JS_TYPE_OBJECT;
+					break;
+				case JSON_TOKEN_ARRAY_START:
+					res = pred->item_type == JS_TYPE_ARRAY;
+					break;
+				case JSON_TOKEN_STRING:
+				case JSON_TOKEN_NUMBER:
+				case JSON_TOKEN_TRUE:
+				case JSON_TOKEN_FALSE:
+				case JSON_TOKEN_NULL:
+					res = pred->item_type == JS_TYPE_SCALAR;
+					break;
+				default:
+					res = false;
+					break;
+			}
+		}
+
+		/*
+		 * Do full parsing pass only for uniqueness check or for JSON text
+		 * validation.
+		 */
+		if (res && (pred->unique_keys || exprtype == TEXTOID))
+			res = json_validate(json, pred->unique_keys, false);
+	}
+	else if (exprtype == JSONBOID)
+	{
+		if (pred->item_type == JS_TYPE_ANY)
+			res = true;
+		else
+		{
+			Jsonb	   *jb = DatumGetJsonbP(js);
+
+			switch (pred->item_type)
+			{
+				case JS_TYPE_OBJECT:
+					res = JB_ROOT_IS_OBJECT(jb);
+					break;
+				case JS_TYPE_ARRAY:
+					res = JB_ROOT_IS_ARRAY(jb) && !JB_ROOT_IS_SCALAR(jb);
+					break;
+				case JS_TYPE_SCALAR:
+					res = JB_ROOT_IS_ARRAY(jb) && JB_ROOT_IS_SCALAR(jb);
+					break;
+				default:
+					res = false;
+					break;
+			}
+		}
+
+		/* Key uniqueness check is redundant for jsonb */
+	}
+	else
+		res = false;
+
+	*op->resvalue = BoolGetDatum(res);
+}
+
+
 /*
  * ExecEvalGroupingFunc
  *
diff --git a/src/backend/jit/llvm/llvmjit_expr.c b/src/backend/jit/llvm/llvmjit_expr.c
index 12d39394b3..daefe66f40 100644
--- a/src/backend/jit/llvm/llvmjit_expr.c
+++ b/src/backend/jit/llvm/llvmjit_expr.c
@@ -1848,6 +1848,12 @@ llvm_compile_expr(ExprState *state)
 				LLVMBuildBr(b, opblocks[opno + 1]);
 				break;
 
+			case EEOP_IS_JSON:
+				build_EvalXFunc(b, mod, "ExecEvalJsonIsPredicate",
+								v_state, op);
+				LLVMBuildBr(b, opblocks[opno + 1]);
+				break;
+
 			case EEOP_AGGREF:
 				{
 					LLVMValueRef v_aggno;
diff --git a/src/backend/jit/llvm/llvmjit_types.c b/src/backend/jit/llvm/llvmjit_types.c
index 315eeb1172..f61d9390ee 100644
--- a/src/backend/jit/llvm/llvmjit_types.c
+++ b/src/backend/jit/llvm/llvmjit_types.c
@@ -133,6 +133,7 @@ void	   *referenced_functions[] =
 	ExecEvalWholeRowVar,
 	ExecEvalXmlExpr,
 	ExecEvalJsonConstructor,
+	ExecEvalJsonIsPredicate,
 	MakeExpandedObjectReadOnlyInternal,
 	slot_getmissingattrs,
 	slot_getsomeattrs_int,
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index 23c7152806..39e1884cf4 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -894,3 +894,22 @@ makeJsonKeyValue(Node *key, Node *value)
 
 	return (Node *) n;
 }
+
+/*
+ * makeJsonIsPredicate -
+ *	  creates a JsonIsPredicate node
+ */
+Node *
+makeJsonIsPredicate(Node *expr, JsonFormat *format, JsonValueType item_type,
+					bool unique_keys, int location)
+{
+	JsonIsPredicate *n = makeNode(JsonIsPredicate);
+
+	n->expr = expr;
+	n->format = format;
+	n->item_type = item_type;
+	n->unique_keys = unique_keys;
+	n->location = location;
+
+	return (Node *) n;
+}
diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
index 69907fbcde..fdb0c6b3fe 100644
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -261,6 +261,9 @@ exprType(const Node *expr)
 		case T_JsonConstructorExpr:
 			type = ((const JsonConstructorExpr *) expr)->returning->typid;
 			break;
+		case T_JsonIsPredicate:
+			type = BOOLOID;
+			break;
 		default:
 			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
 			type = InvalidOid;	/* keep compiler quiet */
@@ -983,6 +986,9 @@ exprCollation(const Node *expr)
 					coll = InvalidOid;
 			}
 			break;
+		case T_JsonIsPredicate:
+			coll = InvalidOid;	/* result is always an boolean type */
+			break;
 		default:
 			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
 			coll = InvalidOid;	/* keep compiler quiet */
@@ -1205,6 +1211,9 @@ exprSetCollation(Node *expr, Oid collation)
 													 * json[b] type */
 			}
 			break;
+		case T_JsonIsPredicate:
+			Assert(!OidIsValid(collation)); /* result is always boolean */
+			break;
 		default:
 			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
 			break;
@@ -1653,6 +1662,9 @@ exprLocation(const Node *expr)
 		case T_JsonConstructorExpr:
 			loc = ((const JsonConstructorExpr *) expr)->location;
 			break;
+		case T_JsonIsPredicate:
+			loc = ((const JsonIsPredicate *) expr)->location;
+			break;
 		default:
 			/* for any other node type it's just unknown... */
 			loc = -1;
@@ -2406,6 +2418,8 @@ expression_tree_walker_impl(Node *node,
 					return true;
 			}
 			break;
+		case T_JsonIsPredicate:
+			return walker(((JsonIsPredicate *) node)->expr, context);
 		default:
 			elog(ERROR, "unrecognized node type: %d",
 				 (int) nodeTag(node));
@@ -3413,6 +3427,16 @@ expression_tree_mutator_impl(Node *node,
 				MUTATE(newnode->coercion, jve->coercion, Expr *);
 				MUTATE(newnode->returning, jve->returning, JsonReturning *);
 
+				return (Node *) newnode;
+			}
+		case T_JsonIsPredicate:
+			{
+				JsonIsPredicate *pred = (JsonIsPredicate *) node;
+				JsonIsPredicate *newnode;
+
+				FLATCOPY(newnode, pred, JsonIsPredicate);
+				MUTATE(newnode->expr, pred->expr, Node *);
+
 				return (Node *) newnode;
 			}
 		default:
@@ -4261,6 +4285,8 @@ raw_expression_tree_walker_impl(Node *node,
 					return true;
 			}
 			break;
+		case T_JsonIsPredicate:
+			return walker(((JsonIsPredicate *) node)->expr, context);
 		default:
 			elog(ERROR, "unrecognized node type: %d",
 				 (int) nodeTag(node));
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index f3ddc34afb..a04c02f58f 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -655,6 +655,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 					json_array_aggregate_order_by_clause_opt
 
 %type <ival>		json_encoding_clause_opt
+					json_predicate_type_constraint
 
 %type <boolean>		json_key_uniqueness_constraint_opt
 					json_object_constructor_null_clause_opt
@@ -754,7 +755,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	RESET RESTART RESTRICT RETURN RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
 	ROUTINE ROUTINES ROW ROWS RULE
 
-	SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
+	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
+	SEQUENCE SEQUENCES
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
 	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
@@ -791,7 +793,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
  * FORMAT_LA, NULLS_LA, WITH_LA, and WITHOUT_LA are needed to make the grammar
  * LALR(1).
  */
-%token		FORMAT_LA NOT_LA NULLS_LA WITH_LA WITHOUT_LA
+%token		FORMAT_LA NOT_LA NULLS_LA WITH_LA WITH_UNIQUE_LA WITHOUT_LA
 
 /*
  * The grammar likewise thinks these tokens are keywords, but they are never
@@ -818,6 +820,12 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %nonassoc	'<' '>' '=' LESS_EQUALS GREATER_EQUALS NOT_EQUALS
 %nonassoc	BETWEEN IN_P LIKE ILIKE SIMILAR NOT_LA
 %nonassoc	ESCAPE			/* ESCAPE must be just above LIKE/ILIKE/SIMILAR */
+
+/* SQL/JSON related keywords */
+%nonassoc	UNIQUE JSON
+%nonassoc	KEYS OBJECT_P SCALAR VALUE_P
+%nonassoc	WITHOUT_LA WITH_UNIQUE_LA
+
 /*
  * To support target_el without AS, it used to be necessary to assign IDENT an
  * explicit precedence just less than Op.  While that's not really necessary
@@ -14850,6 +14858,44 @@ a_expr:		c_expr									{ $$ = $1; }
 														   @2),
 									 @2);
 				}
+			| a_expr IS json_predicate_type_constraint
+					json_key_uniqueness_constraint_opt		%prec IS
+				{
+					JsonFormat *format = makeJsonFormat(JS_FORMAT_DEFAULT, JS_ENC_DEFAULT, -1);
+
+					$$ = makeJsonIsPredicate($1, format, $3, $4, @1);
+				}
+			/*
+			 * Required by SQL/JSON, but there are conflicts
+			| a_expr
+				FORMAT_LA JSON json_encoding_clause_opt
+				IS  json_predicate_type_constraint
+					json_key_uniqueness_constraint_opt		%prec IS
+				{
+					$3.location = @2;
+					$$ = makeJsonIsPredicate($1, $3, $5, $6, @1);
+				}
+			*/
+			| a_expr IS NOT
+					json_predicate_type_constraint
+					json_key_uniqueness_constraint_opt		%prec IS
+				{
+					JsonFormat *format = makeJsonFormat(JS_FORMAT_DEFAULT, JS_ENC_DEFAULT, -1);
+
+					$$ = makeNotExpr(makeJsonIsPredicate($1, format, $4, $5, @1), @1);
+				}
+			/*
+			 * Required by SQL/JSON, but there are conflicts
+			| a_expr
+				FORMAT_LA JSON json_encoding_clause_opt
+				IS NOT
+					json_predicate_type_constraint
+					json_key_uniqueness_constraint_opt		%prec IS
+				{
+					$3.location = @2;
+					$$ = makeNotExpr(makeJsonIsPredicate($1, $3, $6, $7, @1), @1);
+				}
+			*/
 			| DEFAULT
 				{
 					/*
@@ -16406,13 +16452,21 @@ json_output_clause_opt:
 			| /* EMPTY */							{ $$ = NULL; }
 		;
 
+json_predicate_type_constraint:
+			JSON									{ $$ = JS_TYPE_ANY; }
+			| JSON VALUE_P							{ $$ = JS_TYPE_ANY; }
+			| JSON ARRAY							{ $$ = JS_TYPE_ARRAY; }
+			| JSON OBJECT_P							{ $$ = JS_TYPE_OBJECT; }
+			| JSON SCALAR							{ $$ = JS_TYPE_SCALAR; }
+		;
+
 /* KEYS is a noise word here */
 json_key_uniqueness_constraint_opt:
-			WITH UNIQUE KEYS				{ $$ = true; }
-			| WITH UNIQUE				    { $$ = true; }
-			| WITHOUT_LA UNIQUE KEYS		{ $$ = false; }
-			| WITHOUT_LA UNIQUE			    { $$ = false; }
-			| /* EMPTY */ 					{ $$ = false; }
+			WITH_UNIQUE_LA UNIQUE KEYS					{ $$ = true; }
+			| WITH_UNIQUE_LA UNIQUE						{ $$ = true; }
+			| WITHOUT_LA UNIQUE KEYS					{ $$ = false; }
+			| WITHOUT_LA UNIQUE							{ $$ = false; }
+			| /* EMPTY */ 				%prec KEYS		{ $$ = false; }
 		;
 
 json_name_and_value_list:
@@ -17182,6 +17236,7 @@ unreserved_keyword:
 			| ROWS
 			| RULE
 			| SAVEPOINT
+			| SCALAR
 			| SCHEMA
 			| SCHEMAS
 			| SCROLL
@@ -17784,6 +17839,7 @@ bare_label_keyword:
 			| ROWS
 			| RULE
 			| SAVEPOINT
+			| SCALAR
 			| SCHEMA
 			| SCHEMAS
 			| SCROLL
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 737b479f54..4c99dd1dec 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -83,6 +83,7 @@ static Node *transformJsonArrayQueryConstructor(ParseState *pstate,
 												JsonArrayQueryConstructor *ctor);
 static Node *transformJsonObjectAgg(ParseState *pstate, JsonObjectAgg *agg);
 static Node *transformJsonArrayAgg(ParseState *pstate, JsonArrayAgg *agg);
+static Node *transformJsonIsPredicate(ParseState *pstate, JsonIsPredicate *p);
 static Node *make_row_comparison_op(ParseState *pstate, List *opname,
 									List *largs, List *rargs, int location);
 static Node *make_row_distinct_op(ParseState *pstate, List *opname,
@@ -325,6 +326,10 @@ transformExprRecurse(ParseState *pstate, Node *expr)
 			result = transformJsonArrayAgg(pstate, (JsonArrayAgg *) expr);
 			break;
 
+		case T_JsonIsPredicate:
+			result = transformJsonIsPredicate(pstate, (JsonIsPredicate *) expr);
+			break;
+
 		default:
 			/* should not reach here */
 			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(expr));
@@ -3818,3 +3823,74 @@ transformJsonArrayConstructor(ParseState *pstate, JsonArrayConstructor *ctor)
 								   returning, false, ctor->absent_on_null,
 								   ctor->location);
 }
+
+static Node *
+transformJsonParseArg(ParseState *pstate, Node *jsexpr, JsonFormat *format,
+					  Oid *exprtype)
+{
+	Node	   *raw_expr = transformExprRecurse(pstate, jsexpr);
+	Node	   *expr = raw_expr;
+
+	*exprtype = exprType(expr);
+
+	/* prepare input document */
+	if (*exprtype == BYTEAOID)
+	{
+		JsonValueExpr *jve;
+
+		expr = makeCaseTestExpr(raw_expr);
+		expr = makeJsonByteaToTextConversion(expr, format, exprLocation(expr));
+		*exprtype = TEXTOID;
+
+		jve = makeJsonValueExpr((Expr *) raw_expr, format);
+
+		jve->formatted_expr = (Expr *) expr;
+		expr = (Node *) jve;
+	}
+	else
+	{
+		char		typcategory;
+		bool		typispreferred;
+
+		get_type_category_preferred(*exprtype, &typcategory, &typispreferred);
+
+		if (*exprtype == UNKNOWNOID || typcategory == TYPCATEGORY_STRING)
+		{
+			expr = coerce_to_target_type(pstate, (Node *) expr, *exprtype,
+										 TEXTOID, -1,
+										 COERCION_IMPLICIT,
+										 COERCE_IMPLICIT_CAST, -1);
+			*exprtype = TEXTOID;
+		}
+
+		if (format->encoding != JS_ENC_DEFAULT)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 parser_errposition(pstate, format->location),
+					 errmsg("cannot use JSON FORMAT ENCODING clause for non-bytea input types")));
+	}
+
+	return expr;
+}
+
+/*
+ * Transform IS JSON predicate.
+ */
+static Node *
+transformJsonIsPredicate(ParseState *pstate, JsonIsPredicate *pred)
+{
+	Oid			exprtype;
+	Node	   *expr = transformJsonParseArg(pstate, pred->expr, pred->format,
+											 &exprtype);
+
+	/* make resulting expression */
+	if (exprtype != TEXTOID && exprtype != JSONOID && exprtype != JSONBOID)
+		ereport(ERROR,
+				(errcode(ERRCODE_DATATYPE_MISMATCH),
+				 errmsg("cannot use type %s in IS JSON predicate",
+						format_type_be(exprtype))));
+
+	/* This intentionally(?) drops the format clause. */
+	return makeJsonIsPredicate(expr, NULL, pred->item_type,
+							   pred->unique_keys, pred->location);
+}
diff --git a/src/backend/parser/parser.c b/src/backend/parser/parser.c
index 65eb087657..f97d7c3572 100644
--- a/src/backend/parser/parser.c
+++ b/src/backend/parser/parser.c
@@ -237,6 +237,9 @@ base_yylex(YYSTYPE *lvalp, YYLTYPE *llocp, core_yyscan_t yyscanner)
 				case ORDINALITY:
 					cur_token = WITH_LA;
 					break;
+				case UNIQUE:
+					cur_token = WITH_UNIQUE_LA;
+					break;
 			}
 			break;
 
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index dcd2bb2234..49080e5fbf 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -62,6 +62,23 @@ typedef struct JsonUniqueHashEntry
 	int			object_id;
 } JsonUniqueHashEntry;
 
+/* Stack element for key uniqueness check during JSON parsing */
+typedef struct JsonUniqueStackEntry
+{
+	struct JsonUniqueStackEntry *parent;
+	int			object_id;
+} JsonUniqueStackEntry;
+
+/* Context struct for key uniqueness check during JSON parsing */
+typedef struct JsonUniqueParsingState
+{
+	JsonLexContext *lex;
+	JsonUniqueCheckState check;
+	JsonUniqueStackEntry *stack;
+	int			id_counter;
+	bool		unique;
+} JsonUniqueParsingState;
+
 /* Context struct for key uniqueness check during JSON building */
 typedef struct JsonUniqueBuilderState
 {
@@ -1648,6 +1665,110 @@ escape_json(StringInfo buf, const char *str)
 	appendStringInfoCharMacro(buf, '"');
 }
 
+/* Semantic actions for key uniqueness check */
+static JsonParseErrorType
+json_unique_object_start(void *_state)
+{
+	JsonUniqueParsingState *state = _state;
+	JsonUniqueStackEntry *entry;
+
+	if (!state->unique)
+		return JSON_SUCCESS;
+
+	/* push object entry to stack */
+	entry = palloc(sizeof(*entry));
+	entry->object_id = state->id_counter++;
+	entry->parent = state->stack;
+	state->stack = entry;
+
+	return JSON_SUCCESS;
+}
+
+static JsonParseErrorType
+json_unique_object_end(void *_state)
+{
+	JsonUniqueParsingState *state = _state;
+	JsonUniqueStackEntry *entry;
+
+	if (!state->unique)
+		return JSON_SUCCESS;
+
+	entry = state->stack;
+	state->stack = entry->parent;	/* pop object from stack */
+	pfree(entry);
+	return JSON_SUCCESS;
+}
+
+static JsonParseErrorType
+json_unique_object_field_start(void *_state, char *field, bool isnull)
+{
+	JsonUniqueParsingState *state = _state;
+	JsonUniqueStackEntry *entry;
+
+	if (!state->unique)
+		return JSON_SUCCESS;
+
+	/* find key collision in the current object */
+	if (json_unique_check_key(&state->check, field, state->stack->object_id))
+		return JSON_SUCCESS;
+
+	state->unique = false;
+
+	/* pop all objects entries */
+	while ((entry = state->stack))
+	{
+		state->stack = entry->parent;
+		pfree(entry);
+	}
+	return JSON_SUCCESS;
+}
+
+/* Validate JSON text and additionally check key uniqueness */
+bool
+json_validate(text *json, bool check_unique_keys, bool throw_error)
+{
+	JsonLexContext *lex = makeJsonLexContext(json, check_unique_keys);
+	JsonSemAction uniqueSemAction = {0};
+	JsonUniqueParsingState state;
+	JsonParseErrorType result;
+
+	if (check_unique_keys)
+	{
+		state.lex = lex;
+		state.stack = NULL;
+		state.id_counter = 0;
+		state.unique = true;
+		json_unique_check_init(&state.check);
+
+		uniqueSemAction.semstate = &state;
+		uniqueSemAction.object_start = json_unique_object_start;
+		uniqueSemAction.object_field_start = json_unique_object_field_start;
+		uniqueSemAction.object_end = json_unique_object_end;
+	}
+
+	result = pg_parse_json(lex, check_unique_keys ? &uniqueSemAction : &nullSemAction);
+
+	if (result != JSON_SUCCESS)
+	{
+		if (throw_error)
+			json_errsave_error(result, lex, NULL);
+
+		return false;			/* invalid json */
+	}
+
+	if (check_unique_keys && !state.unique)
+	{
+		if (throw_error)
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
+					 errmsg("duplicate JSON object key value")));
+
+		return false;			/* not unique keys */
+	}
+
+	return true;				/* ok */
+}
+
 /*
  * SQL function json_typeof(json) -> text
  *
@@ -1663,21 +1784,18 @@ escape_json(StringInfo buf, const char *str)
 Datum
 json_typeof(PG_FUNCTION_ARGS)
 {
-	text	   *json;
-
-	JsonLexContext *lex;
-	JsonTokenType tok;
+	text	   *json = PG_GETARG_TEXT_PP(0);
+	JsonLexContext *lex = makeJsonLexContext(json, false);
 	char	   *type;
+	JsonTokenType tok;
 	JsonParseErrorType result;
 
-	json = PG_GETARG_TEXT_PP(0);
-	lex = makeJsonLexContext(json, false);
-
 	/* Lex exactly one token from the input and check its type. */
 	result = json_lex(lex);
 	if (result != JSON_SUCCESS)
 		json_errsave_error(result, lex, NULL);
 	tok = lex->token_type;
+
 	switch (tok)
 	{
 		case JSON_TOKEN_OBJECT_START:
diff --git a/src/backend/utils/adt/jsonfuncs.c b/src/backend/utils/adt/jsonfuncs.c
index 7a36f74dad..4c5abaff25 100644
--- a/src/backend/utils/adt/jsonfuncs.c
+++ b/src/backend/utils/adt/jsonfuncs.c
@@ -5665,3 +5665,23 @@ transform_string_values_scalar(void *state, char *token, JsonTokenType tokentype
 
 	return JSON_SUCCESS;
 }
+
+JsonTokenType
+json_get_first_token(text *json, bool throw_error)
+{
+	JsonLexContext *lex;
+	JsonParseErrorType result;
+
+	lex = makeJsonLexContext(json, false);
+
+	/* Lex exactly one token from the input and check its type. */
+	result = json_lex(lex);
+
+	if (result == JSON_SUCCESS)
+		return lex->token_type;
+
+	if (throw_error)
+		json_errsave_error(result, lex, NULL);
+
+	return JSON_TOKEN_INVALID;	/* invalid json */
+}
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 1c078d700d..461735e84f 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -8227,6 +8227,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 		case T_NullTest:
 		case T_BooleanTest:
 		case T_DistinctExpr:
+		case T_JsonIsPredicate:
 			switch (nodeTag(parentNode))
 			{
 				case T_FuncExpr:
@@ -9530,6 +9531,42 @@ get_rule_expr(Node *node, deparse_context *context,
 			get_json_constructor((JsonConstructorExpr *) node, context, false);
 			break;
 
+		case T_JsonIsPredicate:
+			{
+				JsonIsPredicate *pred = (JsonIsPredicate *) node;
+
+				if (!PRETTY_PAREN(context))
+					appendStringInfoChar(context->buf, '(');
+
+				get_rule_expr_paren(pred->expr, context, true, node);
+
+				appendStringInfoString(context->buf, " IS JSON");
+
+				/* TODO: handle FORMAT clause */
+
+				switch (pred->item_type)
+				{
+					case JS_TYPE_SCALAR:
+						appendStringInfoString(context->buf, " SCALAR");
+						break;
+					case JS_TYPE_ARRAY:
+						appendStringInfoString(context->buf, " ARRAY");
+						break;
+					case JS_TYPE_OBJECT:
+						appendStringInfoString(context->buf, " OBJECT");
+						break;
+					default:
+						break;
+				}
+
+				if (pred->unique_keys)
+					appendStringInfoString(context->buf, " WITH UNIQUE KEYS");
+
+				if (!PRETTY_PAREN(context))
+					appendStringInfoChar(context->buf, ')');
+			}
+			break;
+
 		case T_List:
 			{
 				char	   *sep;
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 2419f2b11d..81e78230e4 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202303301
+#define CATALOG_VERSION_NO	202303311
 
 #endif
diff --git a/src/include/executor/execExpr.h b/src/include/executor/execExpr.h
index 53e2c9a467..ea3ac10876 100644
--- a/src/include/executor/execExpr.h
+++ b/src/include/executor/execExpr.h
@@ -236,6 +236,7 @@ typedef enum ExprEvalOp
 	EEOP_HASHED_SCALARARRAYOP,
 	EEOP_XMLEXPR,
 	EEOP_JSON_CONSTRUCTOR,
+	EEOP_IS_JSON,
 	EEOP_AGGREF,
 	EEOP_GROUPING_FUNC,
 	EEOP_WINDOW_FUNC,
@@ -675,6 +676,12 @@ typedef struct ExprEvalStep
 			int			setoff;
 		}			agg_trans;
 
+		/* for EEOP_IS_JSON */
+		struct
+		{
+			JsonIsPredicate *pred;	/* original expression node */
+		}			is_json;
+
 	}			d;
 } ExprEvalStep;
 
@@ -789,6 +796,7 @@ extern void ExecEvalConstraintCheck(ExprState *state, ExprEvalStep *op);
 extern void ExecEvalXmlExpr(ExprState *state, ExprEvalStep *op);
 extern void ExecEvalJsonConstructor(ExprState *state, ExprEvalStep *op,
 									ExprContext *econtext);
+extern void ExecEvalJsonIsPredicate(ExprState *state, ExprEvalStep *op);
 extern void ExecEvalGroupingFunc(ExprState *state, ExprEvalStep *op);
 extern void ExecEvalSubPlan(ExprState *state, ExprEvalStep *op,
 							ExprContext *econtext);
diff --git a/src/include/nodes/makefuncs.h b/src/include/nodes/makefuncs.h
index 50aa00e0c1..06d991b725 100644
--- a/src/include/nodes/makefuncs.h
+++ b/src/include/nodes/makefuncs.h
@@ -112,6 +112,9 @@ extern JsonFormat *makeJsonFormat(JsonFormatType type, JsonEncoding encoding,
 								  int location);
 extern JsonValueExpr *makeJsonValueExpr(Expr *expr, JsonFormat *format);
 extern Node *makeJsonKeyValue(Node *key, Node *value);
+extern Node *makeJsonIsPredicate(Node *expr, JsonFormat *format,
+								 JsonValueType item_type, bool unique_keys,
+								 int location);
 extern JsonEncoding makeJsonEncoding(char *name);
 
 #endif							/* MAKEFUNC_H */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 1764b61cdb..be9c29f0bf 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1583,6 +1583,32 @@ typedef struct JsonConstructorExpr
 	int			location;
 } JsonConstructorExpr;
 
+/*
+ * JsonValueType -
+ *		representation of JSON item type in IS JSON predicate
+ */
+typedef enum JsonValueType
+{
+	JS_TYPE_ANY,				/* IS JSON [VALUE] */
+	JS_TYPE_OBJECT,				/* IS JSON OBJECT */
+	JS_TYPE_ARRAY,				/* IS JSON ARRAY */
+	JS_TYPE_SCALAR				/* IS JSON SCALAR */
+} JsonValueType;
+
+/*
+ * JsonIsPredicate -
+ *		representation of IS JSON predicate
+ */
+typedef struct JsonIsPredicate
+{
+	NodeTag		type;
+	Node	   *expr;			/* subject expression */
+	JsonFormat *format;			/* FORMAT clause, if specified */
+	JsonValueType item_type;	/* JSON item type */
+	bool		unique_keys;	/* check key uniqueness? */
+	int			location;		/* token location, or -1 if unknown */
+} JsonIsPredicate;
+
 /* ----------------
  * NullTest
  *
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 868f389a04..f5b2e61ca5 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -376,6 +376,7 @@ PG_KEYWORD("row", ROW, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("rows", ROWS, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("rule", RULE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("savepoint", SAVEPOINT, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("scalar", SCALAR, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("schema", SCHEMA, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("schemas", SCHEMAS, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("scroll", SCROLL, UNRESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/include/utils/json.h b/src/include/utils/json.h
index b75f7d929d..35a9a5545d 100644
--- a/src/include/utils/json.h
+++ b/src/include/utils/json.h
@@ -26,5 +26,6 @@ extern Datum json_build_object_worker(int nargs, Datum *args, bool *nulls,
 									  bool unique_keys);
 extern Datum json_build_array_worker(int nargs, Datum *args, bool *nulls,
 									 Oid *types, bool absent_on_null);
+extern bool json_validate(text *json, bool check_unique_keys, bool throw_error);
 
 #endif							/* JSON_H */
diff --git a/src/include/utils/jsonfuncs.h b/src/include/utils/jsonfuncs.h
index fc610f6503..a85203d4a4 100644
--- a/src/include/utils/jsonfuncs.h
+++ b/src/include/utils/jsonfuncs.h
@@ -50,6 +50,9 @@ extern bool pg_parse_json_or_errsave(JsonLexContext *lex, JsonSemAction *sem,
 extern void json_errsave_error(JsonParseErrorType error, JsonLexContext *lex,
 							   struct Node *escontext);
 
+/* get first JSON token */
+extern JsonTokenType json_get_first_token(text *json, bool throw_error);
+
 extern uint32 parse_jsonb_index_flags(Jsonb *jb);
 extern void iterate_jsonb_values(Jsonb *jb, uint32 flags, void *state,
 								 JsonIterateStringValuesAction action);
diff --git a/src/interfaces/ecpg/preproc/parse.pl b/src/interfaces/ecpg/preproc/parse.pl
index faeb460ef5..8a3855b4e2 100644
--- a/src/interfaces/ecpg/preproc/parse.pl
+++ b/src/interfaces/ecpg/preproc/parse.pl
@@ -59,6 +59,7 @@ my %replace_string = (
 	'NOT_LA'         => 'not',
 	'NULLS_LA'       => 'nulls',
 	'WITH_LA'        => 'with',
+	'WITH_UNIQUE_LA' => 'with',
 	'WITHOUT_LA'     => 'without',
 	'TYPECAST'       => '::',
 	'DOT_DOT'        => '..',
diff --git a/src/interfaces/ecpg/preproc/parser.c b/src/interfaces/ecpg/preproc/parser.c
index a40f4bef09..30010a5706 100644
--- a/src/interfaces/ecpg/preproc/parser.c
+++ b/src/interfaces/ecpg/preproc/parser.c
@@ -155,6 +155,9 @@ filtered_base_yylex(void)
 				case ORDINALITY:
 					cur_token = WITH_LA;
 					break;
+				case UNIQUE:
+					cur_token = WITH_UNIQUE_LA;
+					break;
 			}
 			break;
 
diff --git a/src/interfaces/ecpg/test/expected/sql-sqljson.c b/src/interfaces/ecpg/test/expected/sql-sqljson.c
index 64784542ed..a2c49b54f9 100644
--- a/src/interfaces/ecpg/test/expected/sql-sqljson.c
+++ b/src/interfaces/ecpg/test/expected/sql-sqljson.c
@@ -100,103 +100,132 @@ main ()
 {
 /* exec sql begin declare section */
    
+   
 
 #line 12 "sqljson.pgc"
  char json [ 1024 ] ;
-/* exec sql end declare section */
+ 
 #line 13 "sqljson.pgc"
+ bool is_json [ 8 ] ;
+/* exec sql end declare section */
+#line 14 "sqljson.pgc"

   ECPGdebug (1, stderr);
 
   { ECPGconnect(__LINE__, 0, "ecpg1_regression" , NULL, NULL , NULL, 0); 
-#line 17 "sqljson.pgc"
+#line 18 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 17 "sqljson.pgc"
+#line 18 "sqljson.pgc"
 
   { ECPGsetcommit(__LINE__, "on", NULL);
-#line 18 "sqljson.pgc"
+#line 19 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 18 "sqljson.pgc"
+#line 19 "sqljson.pgc"

   { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "select json_object ( returning text )", ECPGt_EOIT, 
 	ECPGt_char,(json),(long)1024,(long)1,(1024)*sizeof(char), 
 	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
-#line 20 "sqljson.pgc"
+#line 21 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 20 "sqljson.pgc"
+#line 21 "sqljson.pgc"
 
   printf("Found json=%s\n", json);
 
   { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "select json_object ( returning text format json )", ECPGt_EOIT, 
 	ECPGt_char,(json),(long)1024,(long)1,(1024)*sizeof(char), 
 	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
-#line 23 "sqljson.pgc"
+#line 24 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 23 "sqljson.pgc"
+#line 24 "sqljson.pgc"
 
   printf("Found json=%s\n", json);
 
   { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "select json_array ( returning jsonb )", ECPGt_EOIT, 
 	ECPGt_char,(json),(long)1024,(long)1,(1024)*sizeof(char), 
 	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
-#line 26 "sqljson.pgc"
+#line 27 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 26 "sqljson.pgc"
+#line 27 "sqljson.pgc"
 
   printf("Found json=%s\n", json);
 
   { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "select json_array ( returning jsonb format json )", ECPGt_EOIT, 
 	ECPGt_char,(json),(long)1024,(long)1,(1024)*sizeof(char), 
 	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
-#line 29 "sqljson.pgc"
+#line 30 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 29 "sqljson.pgc"
+#line 30 "sqljson.pgc"
 
   printf("Found json=%s\n", json);
 
   { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "select json_object ( 1 : 1 , '1' : null with unique )", ECPGt_EOIT, 
 	ECPGt_char,(json),(long)1024,(long)1,(1024)*sizeof(char), 
 	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
-#line 32 "sqljson.pgc"
+#line 33 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 32 "sqljson.pgc"
+#line 33 "sqljson.pgc"
 
   // error
 
   { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "select json_object ( 1 : 1 , '2' : null , 1 : '2' absent on null without unique keys )", ECPGt_EOIT, 
 	ECPGt_char,(json),(long)1024,(long)1,(1024)*sizeof(char), 
 	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
-#line 35 "sqljson.pgc"
+#line 36 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 35 "sqljson.pgc"
+#line 36 "sqljson.pgc"
 
   printf("Found json=%s\n", json);
 
   { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "select json_object ( 1 : 1 , '2' : null absent on null without unique returning jsonb )", ECPGt_EOIT, 
 	ECPGt_char,(json),(long)1024,(long)1,(1024)*sizeof(char), 
 	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
-#line 38 "sqljson.pgc"
+#line 39 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 38 "sqljson.pgc"
+#line 39 "sqljson.pgc"
 
   printf("Found json=%s\n", json);
 
-  { ECPGdisconnect(__LINE__, "CURRENT");
-#line 41 "sqljson.pgc"
+  { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "with val ( js ) as ( values ( '{ \"a\": 1, \"b\": [{ \"a\": 1, \"b\": 0, \"a\": 2 }] }' ) ) select js is json \"IS JSON\" , js is not json \"IS NOT JSON\" , js is json value \"IS VALUE\" , js is json object \"IS OBJECT\" , js is json array \"IS ARRAY\" , js is json scalar \"IS SCALAR\" , js is json without unique keys \"WITHOUT UNIQUE\" , js is json with unique keys \"WITH UNIQUE\" from val", ECPGt_EOIT, 
+	ECPGt_bool,&(is_json[0]),(long)1,(long)1,sizeof(bool), 
+	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, 
+	ECPGt_bool,&(is_json[1]),(long)1,(long)1,sizeof(bool), 
+	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, 
+	ECPGt_bool,&(is_json[2]),(long)1,(long)1,sizeof(bool), 
+	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, 
+	ECPGt_bool,&(is_json[3]),(long)1,(long)1,sizeof(bool), 
+	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, 
+	ECPGt_bool,&(is_json[4]),(long)1,(long)1,sizeof(bool), 
+	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, 
+	ECPGt_bool,&(is_json[5]),(long)1,(long)1,sizeof(bool), 
+	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, 
+	ECPGt_bool,&(is_json[6]),(long)1,(long)1,sizeof(bool), 
+	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, 
+	ECPGt_bool,&(is_json[7]),(long)1,(long)1,sizeof(bool), 
+	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
+#line 54 "sqljson.pgc"
 
 if (sqlca.sqlcode < 0) sqlprint();}
-#line 41 "sqljson.pgc"
+#line 54 "sqljson.pgc"
+
+	  for (int i = 0; i < sizeof(is_json); i++)
+		  printf("Found is_json[%d]: %s\n", i, is_json[i] ? "true" : "false");
+
+  { ECPGdisconnect(__LINE__, "CURRENT");
+#line 58 "sqljson.pgc"
+
+if (sqlca.sqlcode < 0) sqlprint();}
+#line 58 "sqljson.pgc"

   return 0;
diff --git a/src/interfaces/ecpg/test/expected/sql-sqljson.stderr b/src/interfaces/ecpg/test/expected/sql-sqljson.stderr
index 907f773eb9..1252cb3b66 100644
--- a/src/interfaces/ecpg/test/expected/sql-sqljson.stderr
+++ b/src/interfaces/ecpg/test/expected/sql-sqljson.stderr
@@ -2,68 +2,90 @@
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ECPGconnect: opening database ecpg1_regression on <DEFAULT> port <DEFAULT>  
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ECPGsetcommit on line 18: action "on"; connection "ecpg1_regression"
+[NO_PID]: ECPGsetcommit on line 19: action "on"; connection "ecpg1_regression"
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 20: query: select json_object ( returning text ); with 0 parameter(s) on connection ecpg1_regression
+[NO_PID]: ecpg_execute on line 21: query: select json_object ( returning text ); with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 20: using PQexec
+[NO_PID]: ecpg_execute on line 21: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_process_output on line 20: correctly got 1 tuples with 1 fields
+[NO_PID]: ecpg_process_output on line 21: correctly got 1 tuples with 1 fields
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_get_data on line 20: RESULT: {} offset: -1; array: no
+[NO_PID]: ecpg_get_data on line 21: RESULT: {} offset: -1; array: no
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 23: query: select json_object ( returning text format json ); with 0 parameter(s) on connection ecpg1_regression
+[NO_PID]: ecpg_execute on line 24: query: select json_object ( returning text format json ); with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 23: using PQexec
+[NO_PID]: ecpg_execute on line 24: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_process_output on line 23: correctly got 1 tuples with 1 fields
+[NO_PID]: ecpg_process_output on line 24: correctly got 1 tuples with 1 fields
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_get_data on line 23: RESULT: {} offset: -1; array: no
+[NO_PID]: ecpg_get_data on line 24: RESULT: {} offset: -1; array: no
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 26: query: select json_array ( returning jsonb ); with 0 parameter(s) on connection ecpg1_regression
+[NO_PID]: ecpg_execute on line 27: query: select json_array ( returning jsonb ); with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 26: using PQexec
+[NO_PID]: ecpg_execute on line 27: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_process_output on line 26: correctly got 1 tuples with 1 fields
+[NO_PID]: ecpg_process_output on line 27: correctly got 1 tuples with 1 fields
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_is_type_an_array on line 26: type (3802); C (1); array (no)
+[NO_PID]: ecpg_is_type_an_array on line 27: type (3802); C (1); array (no)
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_get_data on line 26: RESULT: [] offset: -1; array: no
+[NO_PID]: ecpg_get_data on line 27: RESULT: [] offset: -1; array: no
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 29: query: select json_array ( returning jsonb format json ); with 0 parameter(s) on connection ecpg1_regression
+[NO_PID]: ecpg_execute on line 30: query: select json_array ( returning jsonb format json ); with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 29: using PQexec
+[NO_PID]: ecpg_execute on line 30: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_process_output on line 29: correctly got 1 tuples with 1 fields
+[NO_PID]: ecpg_process_output on line 30: correctly got 1 tuples with 1 fields
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_get_data on line 29: RESULT: [] offset: -1; array: no
+[NO_PID]: ecpg_get_data on line 30: RESULT: [] offset: -1; array: no
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 32: query: select json_object ( 1 : 1 , '1' : null with unique ); with 0 parameter(s) on connection ecpg1_regression
+[NO_PID]: ecpg_execute on line 33: query: select json_object ( 1 : 1 , '1' : null with unique ); with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 32: using PQexec
+[NO_PID]: ecpg_execute on line 33: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_check_PQresult on line 32: bad response - ERROR:  duplicate JSON key "1"
+[NO_PID]: ecpg_check_PQresult on line 33: bad response - ERROR:  duplicate JSON key "1"
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: raising sqlstate 22030 (sqlcode -400): duplicate JSON key "1" on line 32
+[NO_PID]: raising sqlstate 22030 (sqlcode -400): duplicate JSON key "1" on line 33
 [NO_PID]: sqlca: code: -400, state: 22030
-SQL error: duplicate JSON key "1" on line 32
-[NO_PID]: ecpg_execute on line 35: query: select json_object ( 1 : 1 , '2' : null , 1 : '2' absent on null without unique keys ); with 0 parameter(s) on connection ecpg1_regression
+SQL error: duplicate JSON key "1" on line 33
+[NO_PID]: ecpg_execute on line 36: query: select json_object ( 1 : 1 , '2' : null , 1 : '2' absent on null without unique keys ); with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 35: using PQexec
+[NO_PID]: ecpg_execute on line 36: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_process_output on line 35: correctly got 1 tuples with 1 fields
+[NO_PID]: ecpg_process_output on line 36: correctly got 1 tuples with 1 fields
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_is_type_an_array on line 35: type (114); C (1); array (no)
+[NO_PID]: ecpg_is_type_an_array on line 36: type (114); C (1); array (no)
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_get_data on line 35: RESULT: {"1" : 1, "1" : "2"} offset: -1; array: no
+[NO_PID]: ecpg_get_data on line 36: RESULT: {"1" : 1, "1" : "2"} offset: -1; array: no
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 38: query: select json_object ( 1 : 1 , '2' : null absent on null without unique returning jsonb ); with 0 parameter(s) on connection ecpg1_regression
+[NO_PID]: ecpg_execute on line 39: query: select json_object ( 1 : 1 , '2' : null absent on null without unique returning jsonb ); with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 38: using PQexec
+[NO_PID]: ecpg_execute on line 39: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_process_output on line 38: correctly got 1 tuples with 1 fields
+[NO_PID]: ecpg_process_output on line 39: correctly got 1 tuples with 1 fields
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_get_data on line 38: RESULT: {"1": 1} offset: -1; array: no
+[NO_PID]: ecpg_get_data on line 39: RESULT: {"1": 1} offset: -1; array: no
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_execute on line 42: query: with val ( js ) as ( values ( '{ "a": 1, "b": [{ "a": 1, "b": 0, "a": 2 }] }' ) ) select js is json "IS JSON" , js is not json "IS NOT JSON" , js is json value "IS VALUE" , js is json object "IS OBJECT" , js is json array "IS ARRAY" , js is json scalar "IS SCALAR" , js is json without unique keys "WITHOUT UNIQUE" , js is json with unique keys "WITH UNIQUE" from val; with 0 parameter(s) on connection ecpg1_regression
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_execute on line 42: using PQexec
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_process_output on line 42: correctly got 1 tuples with 8 fields
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_get_data on line 42: RESULT: t offset: -1; array: no
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_get_data on line 42: RESULT: f offset: -1; array: no
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_get_data on line 42: RESULT: t offset: -1; array: no
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_get_data on line 42: RESULT: t offset: -1; array: no
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_get_data on line 42: RESULT: f offset: -1; array: no
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_get_data on line 42: RESULT: f offset: -1; array: no
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_get_data on line 42: RESULT: t offset: -1; array: no
+[NO_PID]: sqlca: code: 0, state: 00000
+[NO_PID]: ecpg_get_data on line 42: RESULT: f offset: -1; array: no
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_finish: connection ecpg1_regression closed
 [NO_PID]: sqlca: code: 0, state: 00000
diff --git a/src/interfaces/ecpg/test/expected/sql-sqljson.stdout b/src/interfaces/ecpg/test/expected/sql-sqljson.stdout
index aae052a2b9..558901c406 100644
--- a/src/interfaces/ecpg/test/expected/sql-sqljson.stdout
+++ b/src/interfaces/ecpg/test/expected/sql-sqljson.stdout
@@ -4,3 +4,11 @@ Found json=[]
 Found json=[]
 Found json={"1" : 1, "1" : "2"}
 Found json={"1": 1}
+Found is_json[0]: true
+Found is_json[1]: false
+Found is_json[2]: true
+Found is_json[3]: true
+Found is_json[4]: false
+Found is_json[5]: false
+Found is_json[6]: true
+Found is_json[7]: false
diff --git a/src/interfaces/ecpg/test/sql/sqljson.pgc b/src/interfaces/ecpg/test/sql/sqljson.pgc
index 6a582b5b10..a005503834 100644
--- a/src/interfaces/ecpg/test/sql/sqljson.pgc
+++ b/src/interfaces/ecpg/test/sql/sqljson.pgc
@@ -10,6 +10,7 @@ main ()
 {
 EXEC SQL BEGIN DECLARE SECTION;
   char json[1024];
+  bool is_json[8];
 EXEC SQL END DECLARE SECTION;
 
   ECPGdebug (1, stderr);
@@ -38,6 +39,22 @@ EXEC SQL END DECLARE SECTION;
   EXEC SQL SELECT JSON_OBJECT(1: 1, '2': NULL ABSENT ON NULL WITHOUT UNIQUE RETURNING jsonb) INTO :json;
   printf("Found json=%s\n", json);
 
+  EXEC SQL WITH val (js) AS (VALUES ('{ "a": 1, "b": [{ "a": 1, "b": 0, "a": 2 }] }'))
+	  SELECT
+	  js IS JSON "IS JSON",
+	  js IS NOT JSON "IS NOT JSON",
+	  js IS JSON VALUE "IS VALUE",
+	  js IS JSON OBJECT "IS OBJECT",
+	  js IS JSON ARRAY "IS ARRAY",
+	  js IS JSON SCALAR "IS SCALAR",
+	  js IS JSON WITHOUT UNIQUE KEYS "WITHOUT UNIQUE",
+	  js IS JSON WITH UNIQUE KEYS "WITH UNIQUE"
+		  INTO :is_json[0], :is_json[1], :is_json[2], :is_json[3], :is_json[4],
+		  :is_json[5], :is_json[6], :is_json[7]
+		  FROM val;
+	  for (int i = 0; i < sizeof(is_json); i++)
+		  printf("Found is_json[%d]: %s\n", i, is_json[i] ? "true" : "false");
+
   EXEC SQL DISCONNECT;
 
   return 0;
diff --git a/src/test/regress/expected/sqljson.out b/src/test/regress/expected/sqljson.out
index c4bfe80ba9..d73c7e2c6c 100644
--- a/src/test/regress/expected/sqljson.out
+++ b/src/test/regress/expected/sqljson.out
@@ -754,3 +754,201 @@ CREATE OR REPLACE VIEW public.json_array_subquery_view AS
            FROM ( SELECT foo.i
                    FROM ( VALUES (1), (2), (NULL::integer), (4)) foo(i)) q(a)) AS "json_array"
 DROP VIEW json_array_subquery_view;
+-- IS JSON predicate
+SELECT NULL IS JSON;
+ ?column? 
+----------
+ 
+(1 row)
+
+SELECT NULL IS NOT JSON;
+ ?column? 
+----------
+ 
+(1 row)
+
+SELECT NULL::json IS JSON;
+ ?column? 
+----------
+ 
+(1 row)
+
+SELECT NULL::jsonb IS JSON;
+ ?column? 
+----------
+ 
+(1 row)
+
+SELECT NULL::text IS JSON;
+ ?column? 
+----------
+ 
+(1 row)
+
+SELECT NULL::bytea IS JSON;
+ ?column? 
+----------
+ 
+(1 row)
+
+SELECT NULL::int IS JSON;
+ERROR:  cannot use type integer in IS JSON predicate
+SELECT '' IS JSON;
+ ?column? 
+----------
+ f
+(1 row)
+
+SELECT bytea '\x00' IS JSON;
+ERROR:  invalid byte sequence for encoding "UTF8": 0x00
+CREATE TABLE test_is_json (js text);
+INSERT INTO test_is_json VALUES
+ (NULL),
+ (''),
+ ('123'),
+ ('"aaa "'),
+ ('true'),
+ ('null'),
+ ('[]'),
+ ('[1, "2", {}]'),
+ ('{}'),
+ ('{ "a": 1, "b": null }'),
+ ('{ "a": 1, "a": null }'),
+ ('{ "a": 1, "b": [{ "a": 1 }, { "a": 2 }] }'),
+ ('{ "a": 1, "b": [{ "a": 1, "b": 0, "a": 2 }] }'),
+ ('aaa'),
+ ('{a:1}'),
+ ('["a",]');
+SELECT
+	js,
+	js IS JSON "IS JSON",
+	js IS NOT JSON "IS NOT JSON",
+	js IS JSON VALUE "IS VALUE",
+	js IS JSON OBJECT "IS OBJECT",
+	js IS JSON ARRAY "IS ARRAY",
+	js IS JSON SCALAR "IS SCALAR",
+	js IS JSON WITHOUT UNIQUE KEYS "WITHOUT UNIQUE",
+	js IS JSON WITH UNIQUE KEYS "WITH UNIQUE"
+FROM
+	test_is_json;
+                      js                       | IS JSON | IS NOT JSON | IS VALUE | IS OBJECT | IS ARRAY | IS SCALAR | WITHOUT UNIQUE | WITH UNIQUE 
+-----------------------------------------------+---------+-------------+----------+-----------+----------+-----------+----------------+-------------
+                                               |         |             |          |           |          |           |                | 
+                                               | f       | t           | f        | f         | f        | f         | f              | f
+ 123                                           | t       | f           | t        | f         | f        | t         | t              | t
+ "aaa "                                        | t       | f           | t        | f         | f        | t         | t              | t
+ true                                          | t       | f           | t        | f         | f        | t         | t              | t
+ null                                          | t       | f           | t        | f         | f        | t         | t              | t
+ []                                            | t       | f           | t        | f         | t        | f         | t              | t
+ [1, "2", {}]                                  | t       | f           | t        | f         | t        | f         | t              | t
+ {}                                            | t       | f           | t        | t         | f        | f         | t              | t
+ { "a": 1, "b": null }                         | t       | f           | t        | t         | f        | f         | t              | t
+ { "a": 1, "a": null }                         | t       | f           | t        | t         | f        | f         | t              | f
+ { "a": 1, "b": [{ "a": 1 }, { "a": 2 }] }     | t       | f           | t        | t         | f        | f         | t              | t
+ { "a": 1, "b": [{ "a": 1, "b": 0, "a": 2 }] } | t       | f           | t        | t         | f        | f         | t              | f
+ aaa                                           | f       | t           | f        | f         | f        | f         | f              | f
+ {a:1}                                         | f       | t           | f        | f         | f        | f         | f              | f
+ ["a",]                                        | f       | t           | f        | f         | f        | f         | f              | f
+(16 rows)
+
+SELECT
+	js,
+	js IS JSON "IS JSON",
+	js IS NOT JSON "IS NOT JSON",
+	js IS JSON VALUE "IS VALUE",
+	js IS JSON OBJECT "IS OBJECT",
+	js IS JSON ARRAY "IS ARRAY",
+	js IS JSON SCALAR "IS SCALAR",
+	js IS JSON WITHOUT UNIQUE KEYS "WITHOUT UNIQUE",
+	js IS JSON WITH UNIQUE KEYS "WITH UNIQUE"
+FROM
+	(SELECT js::json FROM test_is_json WHERE js IS JSON) foo(js);
+                      js                       | IS JSON | IS NOT JSON | IS VALUE | IS OBJECT | IS ARRAY | IS SCALAR | WITHOUT UNIQUE | WITH UNIQUE 
+-----------------------------------------------+---------+-------------+----------+-----------+----------+-----------+----------------+-------------
+ 123                                           | t       | f           | t        | f         | f        | t         | t              | t
+ "aaa "                                        | t       | f           | t        | f         | f        | t         | t              | t
+ true                                          | t       | f           | t        | f         | f        | t         | t              | t
+ null                                          | t       | f           | t        | f         | f        | t         | t              | t
+ []                                            | t       | f           | t        | f         | t        | f         | t              | t
+ [1, "2", {}]                                  | t       | f           | t        | f         | t        | f         | t              | t
+ {}                                            | t       | f           | t        | t         | f        | f         | t              | t
+ { "a": 1, "b": null }                         | t       | f           | t        | t         | f        | f         | t              | t
+ { "a": 1, "a": null }                         | t       | f           | t        | t         | f        | f         | t              | f
+ { "a": 1, "b": [{ "a": 1 }, { "a": 2 }] }     | t       | f           | t        | t         | f        | f         | t              | t
+ { "a": 1, "b": [{ "a": 1, "b": 0, "a": 2 }] } | t       | f           | t        | t         | f        | f         | t              | f
+(11 rows)
+
+SELECT
+	js0,
+	js IS JSON "IS JSON",
+	js IS NOT JSON "IS NOT JSON",
+	js IS JSON VALUE "IS VALUE",
+	js IS JSON OBJECT "IS OBJECT",
+	js IS JSON ARRAY "IS ARRAY",
+	js IS JSON SCALAR "IS SCALAR",
+	js IS JSON WITHOUT UNIQUE KEYS "WITHOUT UNIQUE",
+	js IS JSON WITH UNIQUE KEYS "WITH UNIQUE"
+FROM
+	(SELECT js, js::bytea FROM test_is_json WHERE js IS JSON) foo(js0, js);
+                      js0                      | IS JSON | IS NOT JSON | IS VALUE | IS OBJECT | IS ARRAY | IS SCALAR | WITHOUT UNIQUE | WITH UNIQUE 
+-----------------------------------------------+---------+-------------+----------+-----------+----------+-----------+----------------+-------------
+ 123                                           | t       | f           | t        | f         | f        | t         | t              | t
+ "aaa "                                        | t       | f           | t        | f         | f        | t         | t              | t
+ true                                          | t       | f           | t        | f         | f        | t         | t              | t
+ null                                          | t       | f           | t        | f         | f        | t         | t              | t
+ []                                            | t       | f           | t        | f         | t        | f         | t              | t
+ [1, "2", {}]                                  | t       | f           | t        | f         | t        | f         | t              | t
+ {}                                            | t       | f           | t        | t         | f        | f         | t              | t
+ { "a": 1, "b": null }                         | t       | f           | t        | t         | f        | f         | t              | t
+ { "a": 1, "a": null }                         | t       | f           | t        | t         | f        | f         | t              | f
+ { "a": 1, "b": [{ "a": 1 }, { "a": 2 }] }     | t       | f           | t        | t         | f        | f         | t              | t
+ { "a": 1, "b": [{ "a": 1, "b": 0, "a": 2 }] } | t       | f           | t        | t         | f        | f         | t              | f
+(11 rows)
+
+SELECT
+	js,
+	js IS JSON "IS JSON",
+	js IS NOT JSON "IS NOT JSON",
+	js IS JSON VALUE "IS VALUE",
+	js IS JSON OBJECT "IS OBJECT",
+	js IS JSON ARRAY "IS ARRAY",
+	js IS JSON SCALAR "IS SCALAR",
+	js IS JSON WITHOUT UNIQUE KEYS "WITHOUT UNIQUE",
+	js IS JSON WITH UNIQUE KEYS "WITH UNIQUE"
+FROM
+	(SELECT js::jsonb FROM test_is_json WHERE js IS JSON) foo(js);
+                 js                  | IS JSON | IS NOT JSON | IS VALUE | IS OBJECT | IS ARRAY | IS SCALAR | WITHOUT UNIQUE | WITH UNIQUE 
+-------------------------------------+---------+-------------+----------+-----------+----------+-----------+----------------+-------------
+ 123                                 | t       | f           | t        | f         | f        | t         | t              | t
+ "aaa "                              | t       | f           | t        | f         | f        | t         | t              | t
+ true                                | t       | f           | t        | f         | f        | t         | t              | t
+ null                                | t       | f           | t        | f         | f        | t         | t              | t
+ []                                  | t       | f           | t        | f         | t        | f         | t              | t
+ [1, "2", {}]                        | t       | f           | t        | f         | t        | f         | t              | t
+ {}                                  | t       | f           | t        | t         | f        | f         | t              | t
+ {"a": 1, "b": null}                 | t       | f           | t        | t         | f        | f         | t              | t
+ {"a": null}                         | t       | f           | t        | t         | f        | f         | t              | t
+ {"a": 1, "b": [{"a": 1}, {"a": 2}]} | t       | f           | t        | t         | f        | f         | t              | t
+ {"a": 1, "b": [{"a": 2, "b": 0}]}   | t       | f           | t        | t         | f        | f         | t              | t
+(11 rows)
+
+-- Test IS JSON deparsing
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT '1' IS JSON AS "any", ('1' || i) IS JSON SCALAR AS "scalar", '[]' IS NOT JSON ARRAY AS "array", '{}' IS JSON OBJECT WITH UNIQUE AS "object" FROM generate_series(1, 3) i;
+                                                                        QUERY PLAN                                                                        
+----------------------------------------------------------------------------------------------------------------------------------------------------------
+ Function Scan on pg_catalog.generate_series i
+   Output: ('1'::text IS JSON), (('1'::text || (i)::text) IS JSON SCALAR), (NOT ('[]'::text IS JSON ARRAY)), ('{}'::text IS JSON OBJECT WITH UNIQUE KEYS)
+   Function Call: generate_series(1, 3)
+(3 rows)
+
+CREATE VIEW is_json_view AS
+SELECT '1' IS JSON AS "any", ('1' || i) IS JSON SCALAR AS "scalar", '[]' IS NOT JSON ARRAY AS "array", '{}' IS JSON OBJECT WITH UNIQUE AS "object" FROM generate_series(1, 3) i;
+\sv is_json_view
+CREATE OR REPLACE VIEW public.is_json_view AS
+ SELECT '1'::text IS JSON AS "any",
+    ('1'::text || i) IS JSON SCALAR AS scalar,
+    NOT '[]'::text IS JSON ARRAY AS "array",
+    '{}'::text IS JSON OBJECT WITH UNIQUE KEYS AS object
+   FROM generate_series(1, 3) i(i)
+DROP VIEW is_json_view;
diff --git a/src/test/regress/sql/sqljson.sql b/src/test/regress/sql/sqljson.sql
index fbbf6a6d6e..4fd820fd51 100644
--- a/src/test/regress/sql/sqljson.sql
+++ b/src/test/regress/sql/sqljson.sql
@@ -282,3 +282,99 @@ SELECT JSON_ARRAY(SELECT i FROM (VALUES (1), (2), (NULL), (4)) foo(i) RETURNING
 \sv json_array_subquery_view
 
 DROP VIEW json_array_subquery_view;
+
+-- IS JSON predicate
+SELECT NULL IS JSON;
+SELECT NULL IS NOT JSON;
+SELECT NULL::json IS JSON;
+SELECT NULL::jsonb IS JSON;
+SELECT NULL::text IS JSON;
+SELECT NULL::bytea IS JSON;
+SELECT NULL::int IS JSON;
+
+SELECT '' IS JSON;
+
+SELECT bytea '\x00' IS JSON;
+
+CREATE TABLE test_is_json (js text);
+
+INSERT INTO test_is_json VALUES
+ (NULL),
+ (''),
+ ('123'),
+ ('"aaa "'),
+ ('true'),
+ ('null'),
+ ('[]'),
+ ('[1, "2", {}]'),
+ ('{}'),
+ ('{ "a": 1, "b": null }'),
+ ('{ "a": 1, "a": null }'),
+ ('{ "a": 1, "b": [{ "a": 1 }, { "a": 2 }] }'),
+ ('{ "a": 1, "b": [{ "a": 1, "b": 0, "a": 2 }] }'),
+ ('aaa'),
+ ('{a:1}'),
+ ('["a",]');
+
+SELECT
+	js,
+	js IS JSON "IS JSON",
+	js IS NOT JSON "IS NOT JSON",
+	js IS JSON VALUE "IS VALUE",
+	js IS JSON OBJECT "IS OBJECT",
+	js IS JSON ARRAY "IS ARRAY",
+	js IS JSON SCALAR "IS SCALAR",
+	js IS JSON WITHOUT UNIQUE KEYS "WITHOUT UNIQUE",
+	js IS JSON WITH UNIQUE KEYS "WITH UNIQUE"
+FROM
+	test_is_json;
+
+SELECT
+	js,
+	js IS JSON "IS JSON",
+	js IS NOT JSON "IS NOT JSON",
+	js IS JSON VALUE "IS VALUE",
+	js IS JSON OBJECT "IS OBJECT",
+	js IS JSON ARRAY "IS ARRAY",
+	js IS JSON SCALAR "IS SCALAR",
+	js IS JSON WITHOUT UNIQUE KEYS "WITHOUT UNIQUE",
+	js IS JSON WITH UNIQUE KEYS "WITH UNIQUE"
+FROM
+	(SELECT js::json FROM test_is_json WHERE js IS JSON) foo(js);
+
+SELECT
+	js0,
+	js IS JSON "IS JSON",
+	js IS NOT JSON "IS NOT JSON",
+	js IS JSON VALUE "IS VALUE",
+	js IS JSON OBJECT "IS OBJECT",
+	js IS JSON ARRAY "IS ARRAY",
+	js IS JSON SCALAR "IS SCALAR",
+	js IS JSON WITHOUT UNIQUE KEYS "WITHOUT UNIQUE",
+	js IS JSON WITH UNIQUE KEYS "WITH UNIQUE"
+FROM
+	(SELECT js, js::bytea FROM test_is_json WHERE js IS JSON) foo(js0, js);
+
+SELECT
+	js,
+	js IS JSON "IS JSON",
+	js IS NOT JSON "IS NOT JSON",
+	js IS JSON VALUE "IS VALUE",
+	js IS JSON OBJECT "IS OBJECT",
+	js IS JSON ARRAY "IS ARRAY",
+	js IS JSON SCALAR "IS SCALAR",
+	js IS JSON WITHOUT UNIQUE KEYS "WITHOUT UNIQUE",
+	js IS JSON WITH UNIQUE KEYS "WITH UNIQUE"
+FROM
+	(SELECT js::jsonb FROM test_is_json WHERE js IS JSON) foo(js);
+
+-- Test IS JSON deparsing
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT '1' IS JSON AS "any", ('1' || i) IS JSON SCALAR AS "scalar", '[]' IS NOT JSON ARRAY AS "array", '{}' IS JSON OBJECT WITH UNIQUE AS "object" FROM generate_series(1, 3) i;
+
+CREATE VIEW is_json_view AS
+SELECT '1' IS JSON AS "any", ('1' || i) IS JSON SCALAR AS "scalar", '[]' IS NOT JSON ARRAY AS "array", '{}' IS JSON OBJECT WITH UNIQUE AS "object" FROM generate_series(1, 3) i;
+
+\sv is_json_view
+
+DROP VIEW is_json_view;
-- 
2.30.2